<style>
  #expander_container {
    white-space: nowrap;
    width: 3000px;
    position: absolute;
  }

  #positioned_container {
    position: absolute;
    top: 42px;
    left: 42px;
  }
</style>
<div id="expander_container">
  <div id="button1" class="mercury-button">1</div>
  <div id="button2" class="mercury-button mercury-test-button">2</div>
</div>
<div id="positioned_container"></div>